Expression patterns of <i>Mal</i> genes and association with differential maltose and maltotriose transport rate of two <i>Saccharomyces pastorianus</i> yeasts

Beer brewing is a well-known process that still faces great challenges, such as the total consumption of sugars present in the fermentation media. Lager-style beer, a major worldwide beer type, is elaborated by <i>Saccharomyces pastorianus</i> (Sp) yeast, which must ferment high maltotriose content worts, but its consumption represents a notable problem, especially among Sp strains belonging to group I. Factors, such as fermentation conditions, presence of maltotriose transporters, transporter copy number variation, and genetic regulation variations contribute to this issue. We assess the factors affecting fermentation in two Sp yeast strains: SpIB1, with limited maltotriose uptake, and SpIB2, known for efficient maltotriose transport. Here, SpIB2 transported significantly more maltose (28%) and maltotriose (32%) compared with SpIB1. Furthermore, SpIB2 expressed all MAL transporters (Sc<i>MAL</i>x1, Se<i>MAL</i>x1, Sc<i>AGT</i>1, Se<i>AGT</i>1, <i>MTT</i>1, and <i>MPH</i>x) on the first day of fermentation, whereas SpIB1 only exhibited Sc<i>Mal</i>x1, Sc<i>AGT</i>1, and <i>MPH</i>2/3 genes. Some SpIB2 transporters had polymorphic transmembrane domains (TMD) resembling <i>MTT</i>1, accompanied by higher expression of these transporters and its positive regulator genes, such as <i>MAL</i>63. These findings suggest that, in addition to the factors mentioned above, positive regulators of Mal transporters contribute significantly to phenotypic diversity in maltose and maltotriose consumption among the studied lager yeast strains.IMPORTANCEBeer, the third most popular beverage globally with a 90% market share in the alcoholic beverage industry, relies on <i>Saccharomyces pastorianus</i> (Sp) strains for lager beer production. These strains exhibit phenotypic diversity in maltotriose consumption, a crucial process for the acceptable organoleptic profile in lager beer. This diversity ranges from Sp group II strains with a notable maltotriose-consuming ability to Sp group I strains with limited capacity. Our study highlights that differential gene expression of maltose and maltotriose transporters and its upstream trans-elements, such as <i>MAL</i> gene-positive regulators, adds complexity to this variation. This insight can contribute to a more comprehensive analysis needed to the development of controlled and efficient biotechnological processes in the beer brewing industry.